The present invention relates to a computer and, more particularly, to a control circuit for a computer to which at least one peripheral is connected.
Recently, many kinds of computers have been proposed which include a personal computer, a portable computer, and a pocket size computer. To these computers, a peripheral including an external memory, an input device or the like may be connected as an option. For example, a first keyboard is part of the main body of a computer, so that the first keyboard is actuated to input key information. A second keyboard may be connected to the main body of the computer, so that the second keyboard is also actuated to input key information. Otherwise, a memory such as a tape recorder may be connected to the main body of the computer, so that the tape recorder can provide any desired program or data.
For data communication between the computer and the peripheral, conventionally, a signal bus may be provided. In this system, it is advantageous that the peripheral be accessed at the same level as that of the computer. But, it is disadvantageous when the capacity of the signal data bus must be enlarged.
Otherwise, a signal transferring interface circuit may be provided. In this system, it is desirable to make the capacity of necessary signal lines small. But, it is disadvantageous if the data control between the computer and the peripheral is complex. In a computer of the type in which an external keyboard is connected to the computer, a command for reading in key input information must be different between a built-in keyboard and the external keyboard. This requires that some different command be applied during programming to the built-in keyboard and the external keyboard. Therefore, the alternative use of either the built-in keyboard or the external keyboard, in particular, with the same program requires complex control.